Microwave and Low-Frequency Oscillations due to Resonance Instabilities in Ferrites

Abstract

Microwave and low frequency oscillations have been observed in single crystal yttrium iron garnet disks placed in a microwave cavity with an applied dc field normal to the disk. These oscillations occur when the microwave power incident on the cavity exceeds a certain critical value in the milliwatt range. The oscillations occur as sidebands above and below the incident frequency and can also be observed as a modulation of the microwave output of the cavity. The above phenomenon is associated with the ferromagnetic resonance instability due to the fact that the resonant frequency of a disk depends on Mz and thus on the rf magnetic field used to drive it. The combination of the disk and the resonant cavity with high power, provides the conditions necessary for relaxation oscillations to be set up.